As the Republican race heads south for the Alabama and Mississippi primaries this week-two primaries that could be make-or-break contests for Gingrich - rather than a good ol' fashioned welcome, Gingrich is spitting fire at his top GOP rival, saying today that Mitt Romney was the "weakest" frontrunner in nearly a century.

"The fact is, Romney is probably weakest Republican front runner since Leonard Wood in 1920, and Wood lost on the 10th ballot," Gingrich said on "Fox News Sunday."

Wood was the early Republican favorite in the 1920 election, having secured the endorsement from former President Teddy Roosevelt. But despite Wood's monetary advantage, he entered the Republican National Convention without enough delegates to secure the nomination.

After 10 rounds of voting, Republicans dropped Wood and nominated Warren G. Harding, who entered the convention in fourth place in the delegate count.

Gingrich predicted a similar swap could happen this primary cycle. In a brokered convention like that, Gingrich said he thinks "there is a space" for him.

"I think we are likely to see after the last primary in June, we're likely to see a 60-day conversation about what's going to happen as we already see Romney dominating," Gingrich said. "And in that context … remembering that I was in first place both in December and again in mid-January in terms of the Gallup poll and the Rasmussen, I think there is a space for a visionary conservative with big solutions."

Later on CBS' "Face the Nation," Gingrich said he was "committed to going all the way to Tampa," where the Republican National Convention will be held in August.

Gingrich has won only two of the 25 primaries and caucuses so far and is trailing Romney by more than 300 delegates. The pro-Santorum Super PAC, The Red White and Blue Fund, called for Gingrich to drop out so the anti-Romney voting bloc could coalesce around one candidate, Santorum.

But Santorum has not followed in his Super PACs shoes. The candidate said Sunday that "Gingrich can say in as long as he wants."

"I'm not going to tell people to get out," Santorum said on NBC's "Meet the Press." "I didn't ask Speaker Gingrich to get in. I'm not going to ask him to get out."

Santorum also challenged the notion that Romney had the nomination locked up because of his wide delegate lead. According to ABC News estimates, Romney has at least 200 more delegates than Santorum.

"These numbers are going to change dramatically," Santorum said, noting that many of the delegates are unbound and could shift their support to him instead of Romney.